The present invention relates generally to the fabrication of semiconductor devices. More particular, the invention relates to a method and system of removing photoresist or other organic materials from a substrate in a semiconductor manufacture.
Photolithography processes are used in semiconductor manufacture to remove portions of the top layers on a wafer surface and create a desired pattern. Generally, this involves utilizing a polymeric resist that reacts to ultraviolet light, as for example, a novolak/diazonaphtoquinone or novolak/quinonediazide resist.
Typically, this technique involves coating the wafer with a layer of a light-sensitive polymeric photoresist material, transferring the desired pattern formed in a reticle into the photoresist layer, and exposing the photoresist to light (e.g., UV light) to image the pattern on the reticle onto the photoresist layer. This changes the character of the exposed or unmasked portions of the pattern, and the resist layer then undergoes development, for example, using chemical solvents, to selectively remove the unmasked portions of the resist to provide a desired pattern having open areas in the resist layer. Etchants are then applied to remove an underlying substrate, such as silicon, metal or an insulator, that is exposed through the mask openings. Photoresist masks are used in processing steps such as etching, ion implantation, reworks, and high temperature postbakes. After etching is completed, the photoresist layer is no longer needed and must be removed prior to subsequent processing of the wafer. The main object of a photoresist removal is to quickly and completely strip the photoresist without effecting the underlying substrate surface.
There are many conventional resist removal processes that are known to those skilled in the art, including, for example, wet chemical processing and dry plasma etching processing. A typical wet chemical etch involves immersing the wafer in an inorganic resist stripper. A common mixture is a solution of sulfuric acid (H2SO4) and an oxidant such as hydrogen peroxide (H2O2), which attacks organic materials and converts the carbon in the resist to CO2 gas. However, wet cleaning has several drawbacks, including particle generation, difficulties with drying, high expense, and chemical waste disposal. In addition, wet cleaning may require mechanical scrubbing to remove all remnants of the resist.
An alternative to wet cleaning to remove resist and other organic films from a wafer is the use of ozone (O3) as the primary chemical agent. One technique involves exposing the photoresist to an O3-containing gaseous atmosphere while heating the substrate on which the photoresist layer is disposed. The ozone oxidizes the resist and other organics into by-products such as water, carbon monoxide (CO) and carbon dioxide (CO2). Ozone is highly selective to organic materials, and does not etch silicon, silicon dioxide, or aluminum. However, in a gas phase process, ozone must react with the organic material until it volatilizes into a gas phase.
Methods have also been described that utilize ozonated deionized (DI) water to remove resist and resist residues. In one known method, the wafers are immersed in a chilled water bath (about 5xc2x0 C.) and ozone is diffused into the water to strip the resist. A drawback of this method is the low strip rate for the resist.
Another process involves heating the wafers and steam-treating with an ozonated water mixture. A process has also been described in which wafers mounted in a carrier are sprayed with ozonated water within a process chamber. In either process, the resist is stripped as the water runs down the wafer surface. However, such methods do not adequately strip the resist and resist residues from the wafer surface. Additionally, residual resist can remain on the wafer at the contact points between the wafer and the carrier. In the use of spray systems, specific control elements and a more complex system than desirable is needed, and the spray mechanisms may not provide a suitable misting of the wafer surface resulting in poor uniformity of removal.
In another process, the wafers are spun at high revolutions per minute (RPM) and simultaneously sprayed with warm water while ozone is pumped into the reaction chamber. However, it is difficult to maintain a suitably thin layer of water on the surface of the wafer for effective permeation of the ozone to the surface of the wafer.
In view of the foregoing, there is a need for a method of removing photoresist or other organic materials from a substrate that overcomes these problems.
The present invention overcomes the disadvantages of known methods in providing an improved method and system for removing photoresist and, more generally, organic components, from the surface of a substrate such as a semiconductor wafer. The method can be used in conjunction with other compatible methods used for organic material removal.
According to the method of the invention, at least a portion of a wafer or other substrate having an organic component on the surface, is submerged in a solvent, preferably deionized water, and the substrate is then moved relative to the solvent such that a thin layer of solvent is deposited over the organic component on the surface of the substrate, which is then exposed to ozone gas for removal of the organic component.
In one embodiment of the method, the substrate such as a semiconductor wafer is rotated through a solvent section and a gaseous section of the reaction chamber of a cleaning module. Rotation of the wafer through the solvent is controlled so that a thin film or layer of solvent is formed over the organic component on the surface of the substrate which is then exposed to ozone gas in the gaseous section of the reaction chamber. The thickness of the solvent layer is sufficiently thin to facilitate diffusion of the ozone gas therethrough to react with the organic material and remove at least a portion of the organic material from the substrate surface.
As the wafer or other substrate is rotated and passes through the solvent and into the gaseous section, a meniscus of solvent forms at the interface between the solvent and the surface of the wafer, while a thin layer of the solvent is formed over the organic component on the surface of the substrate. Preferably, the ozone gas reacts with the organic component on the surface of the substrate through the meniscus as well as the solvent layer. In addition, water vapor may condense onto the organic component on the surface of the wafer, and the ozone gas can also react with the organic component through the water vapor layer. Gaseous by-products such as CO and CO2 that are formed by the reaction are exhausted from the reaction chamber.
In another embodiment of the method, the substrate can be vertically moved into and out of the solvent section and the gaseous section. Such vertical movement is controlled similarly to the above described rotational movement to form a suitably thin layer of solvent over the organic component on the surface of the substrate as it is drawn upward out of the solvent into the gaseous section whereupon exposure to the ozone gas effectively removes the organic component from the surface of the substrate.
In the use of the method in a semiconductor process, a plurality of semiconductor wafers or other substrates can be loaded into a carrier and moved into a cleaning module that includes a reaction chamber having a gaseous section for containing ozone gas and a section containing a solvent, preferably deionized water, to provide a solvent bath. The solvent section can comprise structure such as a container for holding the solvent therein. The solvent section is adapted to receive the wafer carrier such that the semiconductor wafers are at least partially submerged in the solvent. The solvent section can include a mechanism for contacting the wafer carrier and the semiconductor wafers, and moving the wafers relative to the solvent section and the gaseous section, for example, by vertical or rotational movement. Preferably, the mechanism is operable to rotate the wafers through the solvent and gaseous sections of the reaction chamber. The carrier is loaded into the reaction chamber of the cleaning module and positioned in the solvent such that the wafers are at least partially submerged within the solvent, and the rotating or moving mechanism is placed in contact with the semiconductor wafers. Ozone gas is flowed into the reaction chamber and the moving mechanism is activated to move the wafers through the solvent to form a thin layer of solvent over the organic component on the surface of the wafers and then into the gaseous section to expose the solvent layer to the ozone gas. As the solvent-covered substrate passes through the gaseous section, the ozone gas diffuses through the solvent layer to react with and remove at least a portion of the organic component from the substrate surface.
Also provided is a system embodying a cleaning apparatus for use in the method of the invention. The system includes a reaction chamber comprising a gaseous section for containing ozone gas and a solvent section than can include structure such as a container for holding the solvent. The solvent section is adapted to receive at least one wafer at least partially submerged within the solvent. The system also includes a mechanism to contact and move the substrate relative to the solvent section and the gaseous section, for example by vertical movement and/or preferably by rotational movement. The system further includes a source of ozone gas such as an ozone generator that is in flow communication with the gaseous section of the reaction chamber. The system can further include a conveyor mechanism that moves the wafers or other substrate through the reaction chamber and the solvent, an exhaust pump for removing gaseous by-products from the reaction chamber, and an element for heating the solvent.
Advantageously, the present invention provides an improved method and system for removing substantially all traces of photoresist or other organic components from the surface of a substrate. In addition, the invention provides a method and system for removing organic material that is efficient, low cost, and adaptable to volume semiconductor manufacture. The invention eliminates mechanisms such as spray nozzles and conventional cycling mechanisms, requires fewer control devices than conventional systems, and provides a uniform rate of resist removal.